Producing aluminum powder compacts

ABSTRACT

High density aluminum metal powder compacts are produced without the use of internal lubricants by coating the compacting die walls with a methyl alkyl polysiloxane prior to charging the powder into the die.

United States Patent Storchheim 5] Mar. 18, 1975 54] PRODUCING ALUMINUMPOWDER 3,406,236 10/1968 Kniege 264/338 3,478,136 11/1969 Buchovecky etal. 264/111 COMPACTS [75] Inventor: Samuel Storchheim, Forest Hills,

[73] Assignee: Sinteral Corporation, Jamaica, NY.

[22] Filed: July 8, 1970 [2|] Appl. N0.: 53,289

[52] US. Cl. 75/214, 264/111 [5 l] Int. Cl B22l' 3/12 [58] Field ofSearch 264/111, 39, 338; ll7/5.l, ll7/5.2, 5.3; 75/214 [56] ReferencesCited UNITED STATES PATENTS 3,l32.379 5/1964 Crane 425/DlG. 115

Primary Examiner-D0nald J. Arnold Assistant E.\'aminerJ. R. HallAttorney, Agent, or Firm-Pennie & Edmonds [57] ABSTRACT High densityaluminum metal powder compacts are produced without the use of internallubricants by coating the compacting die walls with a methyl alkylpolysiloxane prior to charging the powder into the die.

2 Claims, N0 Drawings PRODUCING ALUMINUM POWDER COMPACTS This inventionrelates to the art of powder metallurgy of aluminum and, moreparticularly, to the production of aluminum powder compacts forsintering.

In the compacting of aluminum powders preparatory to sintering, it iscommon practice to admix with the powder a lubricant such as a wax or astearate-type soap, or the like, to facilitate compaction. When such alubricant is used, it must be volatilized and removed as completely aspossible during heating-up to sintering temperature so as not tointerfere with the sintering bond. Such lubricants are customarily usedin amounts of about one-half to 3 percent by weight of the metal powder,increasing amounts being used to achieve higher densities, but becauseof the presence of these lubricants in the compacted powder the compactgenerally has a green strength of only about 1,500 p.s.i. and thesintered compact exhibits far less strength and ductility than isexpected of it, the strength and ductility both decreasing withincreasing amount of lubricant. In order to eliminate the need for suchinternal lubricants, the art has resorted to lubrication of thecompacting die walls. In the latter case, the lubricant is generallyapplied in a solvent, and the time required for complete evaporation ofthe solvent has slowed commercial production rates to an uneconomicallevel. Any liquid left in the lubricant on the die walls when the powderis added permits the lubricant surface to break down during compactionwith resulting scoring of the die walls. Consequently all die lubricantsused heretofore for this purpose, including hydrocarbon oils, waxes andsoaps, have not made possible commercialrate production of satisfactoryand uniform green compacts of high density without scoring of the diewalls or of the surfaces of the compacts. This has placed an upper limiton the permissible compacting pressure with the result that the greencompacts often lack the strength to be mechanically ejected from thecompacting die in commercial scale operation and are generallycharacterized by internal voids or laminations, caused at least in partby volatilization of the lubricant, which lead to mechanical failure ofthe sintered part.

I have now discovered that a specific class of polysiloxane lubricants,when used as a die wall lubricant, makes possible the compaction ofaluminum powders without using internal lubricants in the powder. Themethod of producing aluminum metal powder compacts pursuant to thepresent invention comprises forming a bulk mixture of the metal powderin which the particles are in direct metal-to-metal contact, applying tothe walls of a powder-compacting die a coating of a normally liquidmethyl alkyl polysiloxane having a molecular weight between about 1,500and 10,000, then filling the thus-wetted die with said powder, andcompacting the powder in said die.

The method of the invention is applicable to predominantly aluminumpowders the particles of which can be of virtually any size, sizedistribution and shape. Thus, the metal powder can be in excess of 100mesh Tyler Standard or it can be at least 90 percent minus 325 mesh, ormixtures thereof, and the particles can range in shape from chips toneedles to spheres.

The aluminum powder, together with any other metal powder which it maybe desired to combine with the aluminum, is prepared for compacting withonly a single precaution, to wit, the non-use of an internal lubricant.Such a lubricant would preclude a metal-tometal market as Alcoa No. 1220aluminum powder), without contact and interface between the particles ofthe powder. Such contact between the particles is essential to maximumgreen and sintered strength and it is a feature of the present inventionthat any material which would interfere with such a contact is avoided.

The compacting die wall lubricant which makes possible the production ofhigh density green compacts without an internal lubricant or the likecomprises normally liquid methyl alkyl polysiloxanes having molecularweights ranging from about 1,500 to 10,000. The alkyl groups in thesepolysiloxanes include ethyl, propyl, butyl, amyl, hexyl, octyl, decyl,dodecyl and tetradecyl radicals which form long chains of polysiloxaneshaving linear organic radicals ranging from 1 to 40 carbons in length. Afull description of these polysiloxanes appears in The TransActions ofthe American Society of Lubrication Engineers, Volume 9, pages 31-35(1966), in an article by E. D. Brown, Jr., entitled Methyl AlkylSilicones, A New Class of Lubricants.

After the die walls have been coated with the aforementioned lubricant,either by brushing or spraying, or

the like, the thus-wetted die is filled .with sufficient metal powder toform the desired green compact. The powder is then compacted usingsufficient pressure to obtain the desired green density in the compact.The resulting green compact will be characterized, for example, by astrength of at least 5,000 p.s.i. at 93 percent theoretical density, andcan be handled roughly, as with a mechanical die ejector, without dangerof breakage of any sort.

The following specific example is illustrative but not limitative of thepractice of the invention:

A relatively coarse, commercially pure aluminum powder having a particlesize of about 10 percent through 325 mesh Tyler Standard (purchased onthe any additive and thus free from any internal lubricant, was chargedto a die which had been previously spraycoated with a normally liquidmethyl alkyl polysiloxane lubricant purchased on the market as GeneralElectrics Silicone Oil No. SF 1147. The die was designed to produce atiming cover of generally dome shape 2% inches in diameter andone-eighth inch thick. The shape further had a peripheral flangeone-sixteenth inch thick, an angled section and a truncated coneshapedhub. The die was mounted in a conventional two-motion press. Severalhundred such shapes were produced in this manner, each having about 90percent theoretical density at the flanged area, about 85 percenttheoretical density in the dome-shaped portion and about percenttheoretical density in the truncated cone section. No scoring of the dieor of the compacts was observable, and no die-wall erosion or aluminumbuild-up on the die walls could be detected. The green compacts couldnot be broken by hand strength, and none of them broke during mechanicalejection from the green press mold.

The resulting compacts, carried in carbon steel boats, were sintered ina hydrogen atmosphere with a heat-up rate of 40C. per minute to anultimate sintering temperature of about 1,180F. The sintered partsreadily fitted back into the green-press die with only about 1 percentshrinkage, and were then coined to higher density, strength and lustre.

I claim:

1. A process for producing a high density aluminum powder compactcapable of being sintered, said process comprising:

a. forming a bulk metal particle mixture containing predominantlyaluminum metal powder particles wherein the metal particles are indirect metal-tometal contact, said particles ranging in shape from chipsto needles to spheres;

b. applying to the walls of a powder compacting die a coating of anormally liquid methyl alkyl polysiloxane having a molecular weight ofbetween about 1500 and about 10,000, the alkyl radicals in said methylalkyl polysiloxane being selected from the group consisting of linearalkyl radicals ranging from one to 40 carbon atoms in length:

c. charging the mixture of aluminum metal powder particles formed instep (a) to the powder compacting die whose walls have been treated withthe methyl alkyl polysiloxane according to step (b);

d. compacting the aluminum metal powder particles charged to the powdercompacting die in step (c) under pressure to form a green compact havinga strength of at least about 5,000 p.s.i. at 93 percent theoreticaldensity; and

e. sintering the green compact formed in step (d).

2. A process for producing a high density aluminum powder compactcapable of being sintered, said process comprising:

a. forming a bulk metal particle mixture containing predominantlyaluminum metal powder particles wherein the metal particles are indirect metal-tometal contact;

b. applying to the walls of a powder compacting die a coating of anormally liquid methyl alkyl polysiloxane having a molecular weight ofbetween about 1,500 and about 10,000, the alkyl radicals in said methylalkyl polysiloxane being selected from the group consisting of linearalkyl radicals ranging from one to 40 carbon atoms in length;

c. charging the mixture of aluminum metal powder particles formed instep (a) to the powder compacting die whose walls have been treated withthe methyl alkyl polysiloxane according to step (b); and

d. compacting the aluminum metal powder particles charged to the powdercompacting die in step (c) under pressure to form a green compact havinga strength of at least about 5,000 p.s.i. at 93 percent theoreticaldensity.

1. A PROCESS FOR PRODUCING A HIGH DENSITY ALUMINUM POWDER COMPACTCAPABLE OF BEING SINTERED, SAID PROCESS COMPRISING: A. FORMING A BULKMETAL PARTICLE MIXTURE CONTAINING PREDOMINANTLY ALUMINUM METAL POWDERPARTICLES WHEREIN THE METAL PARTICLES ARE IN DIRECT METAL-TO-METALCONTACT, SAID PARTICLES RANGING IN SHAPE FROM CHIPS TO NEEDLES TOSPHERES, B. APPLYING TO THE WALLS OF A POWDER COMPACTING DIE A COATINGOF A NORMALLY LIQUID METHYL ALKYL POLYSILOXANE HAVING A MOLECULAR WEIGHTOF BETWEEN ABOUT 1500 AND ABOUT 10.000, THE ALKYL RADICALS IN SAIDMETHYL ALKYL POLYSILOXANE BEING SELETED ONE THE GROUP CONSISTING OFLINEAR ALKYL RADICALS RANGING FROM TO 40 CARBON ATOMS IN LENGTH, C.CHARGING THE MIXTURE OF ALUMINUM METAL POWDER PARTICLES FORMED IN STEP(A) TO THE POWDER COMPACTING DIE WHOSE WALLS HAVE BEEN TREATED WITH THEMETHYL ALKYL POLYSILOXANE ACCORDING TO STEP (B), D. COMPACTING THEALUMINUM METAL POWDER PARTICLES CHARGED TO THE POWDER COMPACTING DIE INSTEP (C) UNDER PRESSURE TO FORM A GREEN COMPACT HAVING A STRENGTH OF ATLEAST ABOUT 5,000 P.S.I. AT 93 PERCENT THEORETICAL DENSITY, AND E.SINTERING THE GREEN COMPACT FORMED IN STEP (D).
 2. A process forproducing a high density aluminum powder compact capable of beingsintered, said process comprising: a. forming a bulk metal particlemixture containing predominantly aluminum metal powder particles whereinthe metal particles are in direct metal-to-metal contact; b. applying tothe walls of a powder compacting die a coating of a normally liquidmethyl alkyl polysiloxane having a molecular weight of between about1,500 and about 10,000, the alkyl radicals in said methyl alkylpolysiloxane being selected from the group consisting of linear alkylradicals ranging from one to 40 carbon atoms in length; c. charging themixture of aluminum metal powder particles formed in step (a) to thepowder compacting die whose walls have been treated with the methylalkyl polysiloxane according to step (b); and d. compacting the aluminummetal powder particles charged to the powder compacting die in step (c)under pressure to form a green compact having a strength of at leastabout 5,000 p.s.i. at 93 percent theoretical density.